On iOS I don't know, but searching the YT Video with Andisearch you can watch it in the list of search results (in mobile below the chat part), with random proxie and sandboxed.

I like Unwatched but I’m uncertain if its privacy respecting. Most likely isn’t.

I just watch YouTube signed out in Safari. It is very easy to build your algorithm from there. I don't mind the ads since I don't watch YouTube mainly on my phone and I occasionally clear cookies.

You can also install Orion Browser, made by Kagi creators of a privacy focused paid search engine, which supports Firefox extensions like uBLock but I don't think it is open source right now but It will be soon.

Can’t say I have recommendations but would love to hear some as well. Especially an adblocker.

Personally I host a private Invidious instance for my partner and I. We both use the iOS version of Yattee. It’s not great and there are quite a few bugs, both in Invidious and Yattee, but it works well enough for the occasional video. Invidious doesn’t support ads and Yattee has build-in SponserBlock, which works well.

mobileSafari with the Vinegar extension.

Unwatched

I'd say use the website through Safari. Install AdGuard, SponsorBlock, and Vinegar, and it should be smooth sailing. Return YouTube Dislike is available as a UserScript.

Brave and DuckDuckGo also provide nice experiences with YouTube, but thry sadly do not have SponsorBlock or Return YouTube Dislike.

If you really need an app, though, give uYouPlus a try.

YouTube OLED comes with Adblocker, sponsor block, return of dislike button, offline player, or background play and many more features. You can sideload it using Sidestore; however, I’m unsure about its privacy. (That’s what I personally use).